Organ and piano type electrical musical instruments are analogous in use of keyboard operation but have widely different touch dynamics and harmonic content. In the electronic organ type instrument, a key operated switch calls forth one or more voices generated electronically by an electronic oscillator and electrical dividing circuits or by digital arrangements that may use recorded wave forms and repetitive digital readout. Selected notes and/or voices are provided by operator actuation of the keyboard which controls electrical switches that send one or more electronically generated voices to a loudspeaker.
In the most popular electric pianos, a keyboard is provided in which actuation of each key mechanically causes vibration of a reed or tine, which vibration is transduced by a suitable pickup device into an electrical signal and then amplified and converted to sound.
The electronically generated voice and the piano voice each have unique characteristics finding favor with players and listeners. The electromechanical generation of the piano voice, by physically vibrating a reed or tine, provides touch dynamics in the resulting sound, creating an amplitude envelope having attack and decay characteristics uniquely defined in part by mechanical and magnetic configuration of the keyboard and transducer, and in part by the musician. Such touch dynamics are absent from the usual electronically generated voices of the organ type instrument. To provide the pure electronic voices of the organ type instrument with a pianolike sound, various attempts have been made to impose a synthesized amplitude envelope upon the electronically generated voices. Such amplitude envelopes have been partially simulated by various electrical circuits. Others have provided a vibratory reed associated with the tone key and electric circuits to impart amplitude characteristics of the reed to the electronic tone source of an electric organ. These are merely modulated organ voices having no true electric piano sound, nor do they provide satisfactory touch dynamics.
In prior electrical instruments, where a selected amplitude envelope is impressed upon an electronically generated voice, modulating circuits of lesser accuracy, precision and linearity have been employed. Such modulators employ diode circuits of which the linearity is limited at low amplitudes by conduction thresholds of the diodes. Although the amplitude envelope of such a modulator may be such as to provide a very soft or low amplitude sound, the typical diode, because of its conduction threshold, will often provide a sharp cutoff at low amplitude, thus severely compromising desired linearity of such a modulator over the necessary wide range of loudness and providing a sound that is undesirable in many situations.
Accordingly, it is an object of the present invention to provide a new type of keyboard instrument in which both electric piano and electronic voices can be and usually are played together, with extended linearity of modulation. A further object is to permit the piano voice to be generated separately when desired, without any hum or other harmful effect.